Fast polysulfides conversion and regulated lithium plating enabled by W2N quantum dots for high-performance lithium sulfur batteries

Lithium sulfur (Li-S) batteries have been regarded as one of the most promising next-generation batteries. However, the shuttle effect caused by solubility and sluggish kinetics of polysulfides on the cathode and the uneven deposition of lithium on the anode hindered its practical application seriously. Herein, we designed W₂N quantum dots (QW₂N) embedded in mesoporous carbon microspheres (MC) as catalyst (QW₂N/MC) modified on both sides of the separator. The ultrafine QW₂N associated with nitrogen vacancies provide abundant active sites to adsorb the polysulfides and induce the fast in situ conversion, which highly prevent the shuttle effect. Meanwhile, the QW₂N/MC layer on the anode side regulated the uniform deposition of lithium due to the good affinity with lithium ions. In long-term performance evaluations, the Li-S batteries achieved a reversible discharge capacity of 685.4 mAh g⁻¹ after 600 cycles at 1 C with a decay rate as low as 0.07% per cycle. When the sulfur loading was increased to about 7.44 mg cm⁻², it still maintained a high areal capacity of 5.97 mAh cm⁻². This study showed a novel strategy to accelerate the polysulfides conversion and regulate uniform lithium deposition simultaneously by introducing QW₂N modified separators, showing great potential in constructing high-performance Li-S batteries.